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United States Patent |
5,068,265
|
Casey
,   et al.
|
November 26, 1991
|
Sealant composition
Abstract
An anaerobic liquid acrylate sealant composition contains short portions of
one or more types of fibre, particularly aramid fibre pulp, as a filler. A
particulate filler such as fumed silica and/or micronized polyethylene may
also be present. The composition suitably is based on a high proportion of
monofunctional acrylate ester monomer, and a polyacrylate plasticiser. The
composition is used for sealing joints in pipework where it is desired to
seal the joint almost immediately but to allow adjustment of the joint for
at least 24 hours.
Inventors:
|
Casey; Tadhg E. (Dublin, IE);
Melody; David P. (Dublin, IE)
|
Assignee:
|
Loctite (Ireland) Ltd. (Dublin, IE)
|
Appl. No.:
|
384230 |
Filed:
|
July 21, 1989 |
Foreign Application Priority Data
Current U.S. Class: |
523/176; 524/533; 524/538; 525/304; 525/309; 525/420 |
Intern'l Class: |
C09J 004/02 |
Field of Search: |
523/176
524/533,538
525/305,426,304,309,420
521/54
|
References Cited
U.S. Patent Documents
4318959 | Mar., 1982 | Evans et al. | 428/364.
|
4331580 | May., 1982 | Bunyan | 523/176.
|
4439561 | Mar., 1984 | Barber | 524/13.
|
4452944 | Jun., 1984 | Dawdy | 523/176.
|
Foreign Patent Documents |
1422439 | Jan., 1976 | GB.
| |
Other References
Frances et al., "Aramid Pulp Shows Promise as High Performance Thixotrope",
Adhesive Age, Apr. 1988, pp. 27-30.
|
Primary Examiner: Schofer; Joseph L.
Assistant Examiner: Delmendo; R. H.
Attorney, Agent or Firm: Welch, II; Edward K., Miller; Eugene F.
Claims
We claim:
1. An improved anaerobically curable liquid (meth)acrylate ester sealant
composition wherein the improvement comprises employing therein from about
0.1 to about 5% by weight of a fibrillated fibrous filler having a bulk
density of less than about 25 lb. per cubic foot.
2. The improved anaerobic sealant composition of claim 1 wherein the
fibrous filler has a bulk density of less than about 20 lb. per cubic
foot.
3. The improved anaerobic sealant composition of claim 1 wherein the
fibrous filler is present in an amount of from about 0.2 to about 2% by
weight of the composition.
4. The improved anaerobic sealant composition of claim 1 wherein the
fibrous filler is present in an amount of from about 0.25 to about 1% by
weight of the composition.
5. The improved anaerobic sealant composition of claim 1 wherein the
fibrous filler is a polymeric fibre.
6. The improved anaerobic sealant composition of claim 5 wherein the
polymeric fibre is selected from the group consisting of fibrillated
polyethylene fibres, fibrillated aramid fibres, and mixtures of the
foregoing.
7. The anaerobic sealant composition of claim 5 wherein the fibres have a
diameter in the range of about 1 to about 100 micrometres and an average
length in the range of about 0.5 to about 5 millimetres.
8. A composition according to claim 1 wherein the anaerobic composition is
based on a mixture of polymerizable acrylate ester monomers having a low
proportion of polyfunctional acrylate ester, up to 20% by weight of the
total composition, while the remainder of the monomer components comprises
one or more monofunctional acrylate esters.
9. A composition according to claim 8 wherein a plasticiser is present in
an amount from 10 to 80% by weight of the total composition.
10. An improved anaerobically curable liquid (meth)acrylate ester sealant
composition wherein the improvement comprises employing therein an
effective amount of a fibrillated fibre so as to render said anaerobic
sealant composition less susceptible to leaks, prior to cure, than are
found with anaerobic sealant composition of like viscosity but without
said fibrillated fibre.
11. The improved anaerobic sealant of claim 10 wherein the fibre is a
polymeric fibre selected from the group consisting of fibrillated aramid
fibre, fibrillated polyethylene fibre and mixtures of the foregoing.
12. The improved anaerobic sealant composition of claim 11 wherein the
fibre comprises from about 0.1 to about 5% by weight of the composition.
13. The improved anaerobic sealant composition of claim 11 wherein the
fibre comprises from about 0.25 to about 1% by weight of the composition.
14. The anaerobic sealant composition of claim 10 wherein the fibres have a
diameter in the range of about 1 to about 100 micrometres and an average
length in the range of about 0.5 to about 5 millimetres.
15. A composition according to claim 14 wherein the anaerobic composition
is based on a mixture of polymerizable acrylate ester monomers having a
low proportion of polyfunctional acrylate ester, up to 20% by weight of
the total composition, while the remainder of the monomer components
comprises one or more monofunctional acrylate esters.
16. A composition according to claim 15 wherein a plasticiser is present in
an amount from 10 to 80% by weight of the total composition.
17. The improved anaerobically curable liquid (meth)acrylate ester sealant
composition of claim 1, wherein one or more particulate fillers are
present in a weight ratio of from about 6:1 to 40:1, relative to the
amount of fibrillated fibre present.
18. A composition according to claim 17, wherein one or more particulate
fillers are present in a weight ratio of from about 12:1 to 25:1, relative
to the amount of fibrillated fibre present.
Description
BACKGROUND OF THE INVENTION
1) Field of the Invention
This invention relates to sealant compositions, particularly for sealing
joints. It is particularly concerned with anaerobic sealant compositions
used in sealing joints in pipework and other fluid conduits, particularly
joints between interfitting male and female co-axial components,
especially threaded components.
2) Description of the Prior Art
Plumbers currently use a variety of sealants for sealing joints in
pipework. The traditional form of sealant is a combination of a hemp cord
(which is laid in the helical thread of one component) and a linseed oil
formulation known as "bosswhite." This involves an undesirable amount of
manual labour. Anaerobic acrylic resin compositions, which cure
spontaneously when oxygen is excluded as a result of assemble of
interfitting components, are commercially available as pipe sealants, but
they are sometimes criticised on the ground that the composition does not
provide a leak-proof seal in a short enough time. Plumbers wish to be able
to test a joint in pipework under pressure immediately after interfitting
of the components.
Modification of the sealant composition to reduce the cure time is
generally not acceptable because a plumber needs to be able to adjust the
relative angular position of two components by as much as 45.degree. for
some time, at least 24 hours after assembly of the components without
breaking the seal. It is desirable therefore that the sealant composition
should seal the joint almost immediately but should not lock the joint, at
least for 24 hours.
Particulate fillers have been added to such compositions but they tend to
increase the viscosity of the composition to the extent that it is
difficult to apply.
Aramid fibre pulp, such as that sold under the Trademark KEVLAR by E. I. Du
Pont de Nemours & Co., has been described as thixotrope for sealants,
adhesives and coatings (Frances et al, Adhesives Age, April 1988, 27-30)
Frances et al of E. I. Du Pont de Nemours & Co. tested aramid fibre pulp
in a number of adhesives and sealants including epoxy, neoprene, PVC,
plastisol, asphalt, polybutadiene, polyurethane and silicone American
Fillers & Abrasives Inc. of 14 Industrial Park Drive, Bangor, Mich. 49013,
U.S.A. offers KEVLAR pulps for use in adhesives, sealants, coatings, etc.
to give thixotropic properties at low addition levels (Adhesives &
Sealants Newsletter, Mar. 14, 1988). However there is no teaching
concerning the use of aramid fibre pulp in an anaerobic acrylate polymer
composition, or of the effect of such pulp in achieving a rapid seal with
an anaerobic joint sealing composition.
BRIEF SUMMARY OF THE INVENTION
The present invention provides an anaerobic liquid sealant composition
which contains short portions of one or more types of fibre as a filler.
The short portions of fibre may be chopped fibres such as chopped aramid
fibres, polyethylene fibres or carbon fibres. The fibres are preferably
highly fibrillated. It is preferred to use polymeric fibre pulps,
particularly aramid fibre pulps. As described by Frances et al, aramid
fibre pulp comprises very short, highly fibrillated fibres produced by
fracturing the crystalline structure of aramid fibres. The polymeric fibre
may be of the kind described as "expanded" aramid or American Fillers and
Abrasives, Inc. of Bangor, Mich. The fibrillated fibres have curled,
branched and ribbon-like fibrils.
The composition should contain a quantity of the short fibre portions which
is effective in achieving a rapid seal but which is not so great as to
clog an application nozzle or to increase the viscosity of the composition
to a level at which the composition becomes unmanageable and difficult to
apply to components which are to be sealed. A composition viscosity in the
range of about 50,000-500,000 mPa.s or cP is suitable. All viscosities
mentioned in this specification and/or claims are measured on a Brookfield
RVT Viscometer with spindle 7 at 2.5 r.p.m. and at a temperature of
25.degree. C.
The fibres preferably constitute from about 0.1% to 5%, preferably about
0.2%-2%, more particularly about 0.25%-1.0%, by weight of the sealant
composition. The fibres suitably have a diameter in the range from 1 to
100 micrometres, preferably 1-20, more particularly 12-15 micrometres, and
a nominal average length in the range from 0.5 millimetres (preferably 1
mm, more particularly 1.5 mm) to 5 millimetres (preferably 4 mm, more
particularly 2.5 mm). The fibre pulp preferably has a surface area of
about 8-10m.sup.2/ gram and a bulk density of less than about 25
lb./ft..sup.3, preferably less than about 20 lb./ft..sup.3, and most
preferably less than about 15 lb./ft..sup.3.
Short portions of organic and/or inorganic fibres other than aramid or
carbon fibres may also be used. Mixtures of two or more types of fibre may
be used. The fibres should be flexible and not brittle as to avoid or at
least minimize break up in use. They must be compatible with the anaerobic
monomers and with other ingredients in the composition. They must be
acceptable for handling in accordance with recognised Health and Safety
standards. For use on water pipelines, they should also be compatible with
potable water.
It is believed that the incorporation of the fibres into the anaerobic
sealant composition does not affect the curing behaviour of the
composition. However it is believed that when pressure is applied to a
joint immediately after initiation of curing of the composition, the leak
paths which would otherwise develop through the composition are blocked by
a bulking effect of the short fibre portions in the presence of liquid.
This cannot be achieved by the use of particulate fillers alone. Therefore
it is believed that the unexpected advantage achieved by the present
invention is not based on a thixotropic effect of the short fibre portions
but is related to their unique bulking effect. Resistance to "sag" or
"slump" of the composition is not important whereas resistance to leaking
of air under pressure shortly after initiation of curing of the anaerobic
composition is crucial to the success of the invention.
It is however useful to include one or more particulate fillers in the
composition, in addition to the short portions of fibre. Preferred fillers
include fumed silica and/or micronized polyethylene. The particulate
filler may suitably comprise from 1%-20%, preferably 7%-12% by weight of
the sealant composition. The proportions of particulate filler and short
fibre portions relative to one another should be chosen so as to achieve
good flow characteristics and workability. Normally the quantity of
particulate filler should be substantially greater than that of the short
fibre portions, e.g. in a weight ratio of from 6:1 to 40:1, preferably
from 12:1 to 25:1, more particularly about 20:1.
Anaerobic compositions are well known int he art and are generally based on
polymerizable acrylate ester monomers. The term "acrylate" as used herein
includes "methacrylate." At least a portion of the acrylate monomer may be
a di- or other polyacrylate ester. Suitable polyacrylate ester monomers
are di-, tri- and tetraethyleneglycol dimethacrylate; dipropyleneglycol
dimethyacrylate; polyethyleneglycol dimethacrylate; polypropyleneglycol
dimethyacrylate; di(pentamethyleneglycol), dimethacrylate,
tetraethleneglycol diacrylate; tetraethyleneglycol di(chloracrylate);
diglycerol diacrylate; diglycerol tetramethacrylate; tetramethylene
dimethacrylate; ethylene dimethacrylate; butyleneglycol dimethacylate;
neopentylglycol diacrylate; and trimethylolpropane triacrylate. General
reference is made to U.S. Pat. Nos. 3,041,322; 33,043,820; 3,046,262;
3,300,547; 3,425,988and 3,435,012, incorporated herein by reference.
Suitable anaerobic sealant compositions may also contain a higher
proportion of monofunctional acrylate esters (esters containing one
acrylate group) than is typically found with anaerobic adhesives or
impregnation compositions. Preferably the monofunctional esters are those
with a relatively polar alcoholic moiety. Typical examples of compounds
within this category are 3-phenyl propyl methacrylate;
cyclohexylmethacrylate; tetrahydrofurfuryl methacrylate; hydroxethyl
acrylate; hydroxypropyl methacrylate; t-butylaminoethyl methacrylate;
cyanoethylacrylate and chloroethyl methacrylate.
Particularly suitable anaerobic compositions are described in European
Patent Application EP 0,140,006 A2, incorporated herein by reference, of
Dr. Gerhard Piestert which relates to sealants comprising polymerisable
monomer components, a permanent adhesive substance and an initiator
system. The monomer components have a low proportion of polyfunctional
acrylate esters, up to 20% by weight of the total composition, while the
remainder of the monomer components comprises one or more monofunctional
acrylate esters. The monofunctional acrylate ester preferably comprises
10%-89% by weight of the composition, more particularly 19%-35% by weight,
while the polyfunctional acrylate ester preferably comprises 1%-10% by
weight of the composition. The permanent adhesive substance, which is
dissolved in the monomers, and which may be present in an amount from 10
to 80% by weight, preferably 35 to 60% by weight, of the total
composition, preferably comprises a polyacrylate such as the poly(butyl
acrylate) which is commercially available from BASF (Badische Anilin- &
Soda-Fabrik AG) under the Trademark ACRONAL 4F. This polyacrylate, which
is of relatively low molecular weight, is fluid at room temperature; as a
50% solution in ethyl acetate it has a viscosity at 20.degree. C.
(according to DIN53211, 4 mm orifice) of 40-60 secs, and behaves as a
polymeric plasticiser.
Another class of polyacrylate ester monomers utilized in anaerobic sealant
compositions are the isocyanate monoacrylate reaction products described
in U.S. Pat. No. 3,424,988 of Toback and Gorman, issued 4th Feb. 1969,
incorporated herein by reference.
In addition to the monomers and (where appropriate) plasticiser, an
anaerobic composition normally contains an initiator (particularly a
peroxy compound), and an accelerator (particularly an amine) and a
stabilizer. General reference is made to British Patent GB 1,422,439,
incorporated herein by reference. Other ingredients which are also
conventionally added to anaerobic sealant compositions such as
plasticisers and pigments may also be present. In the composition of the
present invention, a plasticiser or extender of the kind described in EP
0,140,006 A2 which is a low molecular weight viscous liquid is preferably
present.
The anaerobic sealant composition of the present invention may be prepared
by any of the known methods in the art.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The invention is illustrated in the following Examples.
EXAMPLE 1
An anaerobic sealant composition (hereafter called "Y") was made up as
follows:
______________________________________
% W/W
______________________________________
Methacrylate monomer A
27.0
Methacrylate monomer B
3.0
Plasticizer (ACRONAL 4F)
56.0
Cumene Hydroperoxide (90%)
1.0
Saccharin 1.0
1,2,3,4-Tetrahydro quinoline
0.5
Stabilizer 1.0
Pigment 0.5
Particulate filler 9.5
Dry Aramid fibre pulp
0.5
______________________________________
The methacrylate monomers A and B were 3-Phenylpropyl -methacrylate and
ethylene glycol dimethacrylate respectively.
The plasticiser was ACRONAL 4F from BASF which has been described above.
The stabiliser was 2% 1,4-Naphthoquinone in polyethylene dimethacrylate.
The pigment was titanium dioxide paste in polyester commercially available
from Pigment Dispersions Inc., N.J., U.S.A. as PDI 1100. The particulate
filler was equal parts of fumed silicon dioxide and micronized
polyethylene.
The aramid fibre pulp was obtained from E. I. Du Pont de Nemours & Co. Inc.
Under the Trademark KEVLAR Merge 6F128 Dry Pulp.
According to published Du Pont information it has the following properties:
______________________________________
Dry Pulp
Merge 6F218
______________________________________
+14 Mesh 4 .+-. 2
-13 + 30 Mesh 17 .+-. 3
-30 + 50 Mesh 33 .+-. 5
-50 + 100 Mesh 26 .+-. 2
-100 Mesh 20 .+-. 4
Canadian Std. Freeness
300-425
Nominal Average Length
Approx. 2 mm
BET Surface Area, m.sup.2 /g
10
Moisture, % 4-7
Bulk Density, lbs/cu. ft.
9
______________________________________
A similar composition (hereafter called "Z") was made up with 2% w/w aramid
fibre pulp. A similar composition without any aramid fibre pulp (hereafter
called "X") was used for comparative purposes.
The compositions prepared as above were used in pipe sealing tests on 0.75
inch (19 mm) mildsteel threaded pip fittings. The liquid composition was
applied to the male fittings in conventional manner, and the male fitting
was then screwed into the female fitting, as a result of which the curing
of the anaerobic composition was initiated. Each of the compositions cured
to an elastic-plastic consistency, somewhat similar to chewing gum.
Air pressure was applied to the joint, which was held in a reservoir of
water. The pressure was held for approximately 1 minute and observations
were made as to whether any air bubbles escaped from the joint into the
water. Two series of tests were carried out, one series immediately after
assembly of the fittings and the second series 1 hour after assembly of
the fittings. The results are set out below:
______________________________________
Formulation
Time to Test
Result
______________________________________
X Immediate Failure at less than 1 Bar
Y Immediate 4 out of 6 samples passed at
2 Bar
Z Immediate 5 out of 6 samples passed at
2 Bar+
X 1 hour Failure at 2 Bar
Y 1 hour All samples passed at 6 Bar
Z 1 hour All samples passed at 6 Bar
______________________________________
+One sample failed due to a loose fitting.
1 Bar = 0.1 MPa.
All of the joints remained adjustable for 24 hours after assembly. In the
case of compositions Y and Z, the seal was re-established immediately
after adjustment.
EXAMPLE 2
In order to demonstrate that the improvement in sealing capability as a
result of adding fibre pulp was not due to an increase in thickening of
the composition, the following further compositions having a viscosity of
the order of 200,000 mPa.s were prepared. Composition A was similar to
composition Y but it contained no Aramid fibre pulp. The quantity of
filler was increased by about 1% w/w as compared to composition Y. This
composition had a viscosity of 184,000 mPa.s.
Composition B was also similar to Composition Y but the particulate filler
was omitted and the quantity of dry Aramid fibre pulp was increased to
1.5% w/w. This composition had a viscosity of 204,000 mPa,s, It was
relatively difficult to handle because of dryness.
Composition Y has a viscosity of 184,000 mPa.s. For experimental purposes,
viscosities of 184,000 mPa.s and 204,000 mPa.s are regarded as similar.
Sealing capability was tested using a laboratory rig with a set fixed gap,
rather than a threaded fitting which may have a variation in the gap which
the product has to seal. The laboratory rig consists of an aluminum base
with a flat circular flange having 100 mm outside diameter and a flange
width of 10 mm. Each composition was applied to this flange face and the
seal was completed by a flat glass plate which was placed over the flange
and clamped at a gap of 0.125 mm.
A pressure of 1.5 p.s.i. over atmospheric was applied inside the rig and
the time taken for the leak path to develop after assembly of the rig
(i.e. clamping of the flat glass plate) was determined by observation
through the glass.
The results were as follows:
______________________________________
Time to Leak
Composition Test 1 Test 2
______________________________________
A 20 seconds
15 seconds
B 50 seconds
55 seconds
Y 70 seconds
______________________________________
Comparison of compositions B and Y against Composition A shows the
advantage achieved by addition of the fibre pulp in compositions of
similar viscosity.
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